- Inode and dcache Hash table only needs half the memory/cache because
   of using hlists.
 - Simplify dcache-rcu code.  With NULL end markers in the hlists
   is_bucket is not needed anymore.  Also the list walking code
   generates better code on x86 now because it doesn't need to dedicate
   a register for the list head.
 - Reorganize struct dentry to be more cache friendly.  All the state
   accessed for the hash walk is in one chunk now together with the
   inline name (all at the end)
 - Add prefetching for all the list walks.  Old hash lookup code didn't
   use it.
 - Some other minor cleanup.